Methods, systems and apparatus for regulating frequency of generated power using flywheel energy storage systems with varying load and/or power generation

ABSTRACT

Featured are methods for regulating the AC frequency of the electrical power be supplied on an electrical distribution system or grid. Such a method includes electrically coupling an energy storage sub-system to the electrical distribution network, where the energy storage sub-system includes one or more flywheel energy storage systems. Also featured as devices, systems and apparatuses embodying such methodologies or for use in implementing such methodologies of the present invention.

FIELD OF INVENTION

The present invention relates to methods, systems and apparatuses for regulating the frequency of the generated power when the load and/or generated power is subject to variation as a function of time, in particular methods, systems and apparatuses for regulating frequency of generated electrical power when the load and/or power being generated varies as a function of time and more particularly, methods, systems and apparatuses for regulating frequency of generated electrical power when the load and/or power being generated varies as a function of time using one or more flywheel energy storage systems.

BACKGROUND OF THE INVENTION

In the United States, electric power is generated so as to provide an AC voltage in a desired voltage range and at a desired frequency, 60 Hz. Such power is generated by anyone of a number of power generation plants or power generation methods including for example large fixed electrical power generation facilities using fossil fuel (e.g., natural gas, coal, or fuel oil) or nuclear energy to generate electricity, hydroelectric power generation facilities, and pumped hydroelectric power generation facilities. The particular mixture of electrical power generation facilities that are to be operated at any given time are selected based on cost and other factors including regulating the grid voltage as to be within a desired range and regulating the frequency of the AC voltage so as to be at or about the desired frequency.

There is shown in FIG. 1A, an exemplary daily load curve that illustrates the variation as a function of time of the electrical load that is created by users and imposed on the electrical grid or electrical generation and distribution system that interconnects the power generation facilities and the various electrical load sources. Such electrical load sources include households, businesses, manufacturing facilities, computer facilities, and transportation services (e.g., mass transit systems powered by electricity). Although the curve illustrated in FIG. 1A suggests that the load changes occur over a large time period, in actuality load changes are extremely rapid (e.g., subsecond) as the various electrical power users or consumers adjust their individual electrical power requirements. There is shown in FIG. 1B an exemplary load curve 5 that illustrates the short-term variation in the daily load illustrated in FIG. 1A between the hours of midnight and 3 AM.

Because of such short-term variations that occur in the electrical load imposed on the electrical generation and distribution system and because the ability of a generator to follow such load variations is typically much slower than the time period of the load variation, the electrical generation and distribution system is constantly challenged with a mismatch between the load and the power being generated. As is known in the art, when the electrical load exceeds the total power being generated, the system the AC frequency drops. Alternatively, when the total power being generated exceeds the electrical load requirement, the frequency rises.

There is shown in FIG. 2, an exemplary curve that illustrates the variation in AC frequency as a function of time over a 24 hour time period. As illustrated, the mean AC frequency is 60.002 Hz, the maximum AC frequency is 60.063 Hz, and the minimum AC frequency is 59.944 Hz. ill a number of applications, such changes in AC frequency cannot be tolerated and so the power producer or consumer must install a system that is interconnected to the input from the electrical output generation and distribution system and that locally regulates the AC frequency so as to be within a desired range or at a desired value.

Consequently, the power output of the electrical generation equipment is being constantly adjusted so as to match the total power being consumed by or lost to the transmission and distribution and consumed by the customer load(s). In order to keep both the voltage and AC frequency within desired limits and/or ranges, the difference between the load and the power being generated is determined periodically and this difference is used to increase or decrease the output of the generators/power generation facilities. In this regard, and as known to those skilled in the art, real power generation/absorption is associated with frequency regulation and reactive power generation/absorption is associated with voltage regulation.

More particularly, a regional dispatching location or center is tasked with monitoring load and power generation as well as other factors (e.g., correction for frequency shift or time error) and outputs a control/dispatch signal (e.g., sometimes referred to as an energy management system (EMS) signal) to one or more generators/power generation facilities to increase or decrease the power output of such generators/power generation facilities. According to one technique, a large number of monitoring points or nodes are defined for a given area and the dispatching location or center monitors each of the monitoring points as to the foregoing factors. In addition and as described further herein, such a determination also can result in additional generating capacity being brought on-line so as to increase the total generating capacity of the power generation and distribution system or to take on-line generating capacity off-line, or put it in a standby on-line condition, so as to decrease the total generating capacity of the power generation and distribution system.

For example, a determination is made of the difference between the load and power generation, and a control/correction signal is outputted periodically (e.g., every 2-4 seconds) to the power generator/power generation facility(s). Because of the time lag associated with increasing or decreasing power by a given power generator, however, the effect on power generation by the signal being in outputted is delayed in time. There is shown in FIGS. 3A,B, generation and load curves that illustrate the responsiveness of a fossil-fuel power generator (FIG. 3A) and a pumped Hydro power generator (FIG. 3B) to a varying load.

As implemented in most electric power grids, regulation is a function or parameter that involves the use of on-line generation that is equipped with automatic generation control (AGC) and that can change output quickly (MW/minute) to track the moment-to-moment fluctuations in customer loads and to correct for the unintended fluctuations in generation. In so doing, regulation helps to maintain interconnection frequency, manage differences between actual and scheduled power flows between control areas, and match generation to load within the control area. Regulation requires faster response than can be obtained from units responding to market signals alone. Generators offer capacity that can be controlled by the system operator's AGC system to balance the power system.

One methodology for determining the amount of regulatory power demand uses an area control error (ACE) score. Such a method typically determines the ACE by comparing the power being delivered and the power required. In addition, the ACE being generated can also take into consideration corrections for frequency shift and/or other minor corrections such as a time error and a manual adjustment. In this method, as the ACE value rises or lowers, the regulation power being provided is adjusted accordingly. A low ACE score typically means that the power generation in distribution system is close to optimal operation from the standpoint of AC frequency. There is shown in FIG. 3C, an illustration of an algorithm of one technique for determining an ACE.

Control areas are not able and not required to perfectly match generation and load. The National Electricity Reliability Council (NERC) has established the Control Performance Standard (CPS) to determine the amount of imbalance that is permissible for reliability purposes. CPS 1 measures the relationship between the control area's area control error (ACE) and the interconnection frequency on a 1-minute average basis. NERC requires control areas to restore the generation/load balance within 15 minutes. Reserve service definitions require full reserve response within 10 minutes. The additional 5 minutes is provided for the system operator to assess the situation and respond.

CPS1 values can be either “good” or “bad.” When frequency is above its reference value, under-generation benefits the interconnection by lowering frequency and leads to a good CPS 1 value. Over-generation at such times, however, would further increase frequency and lead to a bad CPS1 value. CPS1, although recorded every minute, is evaluated and reported on an annual basis. NERC sets minimum CPS1 requirements that each control area must exceed each year.

CPS2, a monthly performance standard, sets control-area-specific limits on the maximum average ACE for every 10-minute period. Control areas are permitted to exceed the CPS2 limit no more than 10% of the time. This 90% requirement means that a control area can have no more than 14.4 CPS2 violations per day, on average, during any month.

Typically, approximately one percent (1%) of the power being transmitted and/or capable of being generated and delivered to the utility grid or electrical distribution system is reserved to fine tune or regulate the AC frequency of the electrical power being distributed. Such a source of electrical power is typically maintained in an on-line status with respect to the generation and distribution system, so as to be capable of supplying electric power at full capacity typically within at least a predetermined time period of a request for such power production. In present day applications the predetermined time period is typically about five minutes. Also, present regulatory standards for the generation of electrical power (e.g., standards set by FERC or NERC) require that the distribution system be balanced at least once every ten minutes and that over time the over and under generation nets to zero (0). As a result the correction typically can command a generator to alternatively load and then un-load hundreds of time a day. Although such a mode of operation is achievable with some types of power generating facilities, such a mode of operation has a negative impact on the life and overall deficiency of a typical fossil-fueled electrical generator (e.g., gas turbine powered electric generator).

In some cases, battery farms have been established and configured so as to have electrical capacities on the order of 500 kW to about 40 MW. While batteries are used to form an un-interruptible power supply, cyclical operation of a battery such as that undergone when performing fine tune regulation of AC frequency can prove to be damaging to the battery, including affecting operational life as well as the battery storage capacity.

In addition, the power dispatcher also can use the determined power difference to determine if supplemental or replacement reserve capacities should be brought online to increase the power generation capability of the power generation and distribution system. For major deviations from the desired or nominal AC frequency (e.g. 60 Hz), the dispatcher would output a signal and/or a request to bring spinning reserves that are typically on-line up to power and/or a signal/request to bring supplemental, and/or replacement reserve capacity on-line. Such reserves are typically capable of providing larger blocks of power as a complement to the power sources utilized for fine tuning of the AC frequency, however, such reserves typically take a longer time to reach full capacity (e.g., on the order of 10-15 or 30-60 minutes) and thus are not practically speaking useable for the fine tune regulation of AC frequency.

It thus would be desirable to provide new methods, systems and apparatuses for regulating AC frequency of the electrical power being generated. It would be particularly desirable to provide such methods, systems and apparatuses that can regulate AC frequency with a faster response as compared to conventional/prior art methods, systems and apparatuses and in a environment where load changes are highly variable or cyclical. It also would be particularly desirable to provide such methods, systems and apparatuses that embody one or more flywheel energy storage systems as the mechanism for regulating AC frequency. It also would be particularly desirable to provide such methods, systems and apparatuses that embody one or more flywheel energy storage systems in combination with a switchable load as a mechanism for regulating AC frequency. It also would be particularly desirable for such methods, systems and apparatuses to be adapted for use with existing methodologies, systems and apparatuses for determining and/or correcting for the difference between power generation and load. It also would be particularly desirable for such systems and apparatuses to be easily integrated or adapted for use with existing electrical power distribution systems.

SUMMARY OF THE INVENTION

The present invention features methods for regulating, more particularly the fine tune regulation, of the AC frequency of the electrical power be supplied on an electrical distribution system or grid. Also featured are devices, systems and apparatuses embodying such methodologies or for use in implementing such methodologies of the present invention.

According to one aspect of the present invention, there is featured a method for controlling AC frequency of the electrical power being distributed to an electrical power distribution network, which network is connected to one or more loads and to one or more power sources. Such a method includes electrically coupling an energy storage sub-system to the electrical distribution network, where the energy storage sub-system includes one or more flywheel energy storage systems and controlling the operation of each of the flywheel energy storage systems, responsive to total power being outputted by the one or more power sources and a total load imposed by the one or more loads and line losses associated with the transmission and distribution network, so the electrical storage subsystem outputs an amount of electrical energy to the electrical distribution network so as to regulate the AC frequency of the electrical power being distributed to the electrical distribution network so as to be at or about a desired AC frequency. The energy storage subsystems can be located at one or more locations throughout the transmission and distribution network, at load sites and at generating facilities so as to regulate AC frequency.

In more particular embodiments, the energy storage sub-system includes a plurality or more of flywheel energy storage systems, a multiplicity or more of flywheel energy storage systems, four or more flywheel energy storage systems, 4 to 10 flywheel energy storage systems, 10 flywheel energy storage systems, 10 or more flywheel energy storage systems that are electrically coupled to electrical distribution network. The number of flywheel energy storage systems making up the energy storage sub-system and thus being electrically coupled to the electrical distribution network, is sufficient so the so-configured energy storage sub-system or the array of flywheel energy storage systems should provide the desired power output for the desired amount of time and at the desired output voltage. In more specific embodiments, the method includes arranging the flywheel energy storage systems at a given location so as to form an array of such flywheel energy storage systems and wherein the array is electrically coupled to the electrical distribution network.

In more particular embodiments, such a frequency control method includes controlling the operation of each of the flywheel energy storage systems so as to reduce the amount of power being outputted to the electrical distribution network by the energy storage sub-system a determined amount, when the total power being outputted by the one or more power sources exceeds the total load imposed by the one or more loads and the line losses associated with the transmission and distribution network. In addition, the flywheel energy storage systems can be operated so as to draw power from the distribution network when there is an excess of electrical power that is being generated. In this way, the energy storage sub-system can absorb at least a portion of the excess electrical energy being generated.

Such a frequency control method also includes increasing the amount of power being outputted to the electrical distribution network by the energy storage sub-system by another determined amount, when the total power being outputted is less than the total load. Stated another way, the flywheel energy storage systems can be operated so as to provide electrical power to the distribution network when the electrical power being generated is less than that required to power all the loads that are connected to the network and to account for line losses. In such a case, the another determined amount is determined by evaluating a difference between the total power and the total load. Because of the controllability of the flywheel energy storage systems, the energy storage sub-system can be controlled so as to control the amount of energy being distributed to or being drawn from the network.

In the foregoing, the determined amount and the another determined amount are determined by evaluating a difference between the total power and the total power consumed (i.e., load plus line losses). In more particular embodiments, the difference between the total power and the total load is determined periodically and said controlling includes controlling operation of each of the one or more flywheel energy storage systems responsive to the periodically determined difference.

In yet another embodiment, the frequency control methodology includes determining a difference between the total power being outputted by the one or more power sources and the total load imposed by the one or more loads. Such a methodology also includes controlling the operation of each of the flywheel energy storage systems of the energy storage sub-system so as to maintain the AC frequency at or about a desired value by one of: increasing power being outputted by one or more flywheel energy storage systems when the determined difference is a negative value, or decreasing power being outputted by the one or more FESS energy storage sub-system when the determined difference is a positive value.

In further embodiments, a frequency control methodology according to the present invention includes electrically coupling a plurality of energy storage sub-systems to the electrical distribution network and separately controlling each of the energy storage sub-systems so as to one of deliver electrical power to the electrical distribution network or absorb electrical power from the electrical distribution network. In further embodiments, such a methodology includes controllably operating the flywheel energy storage systems of each of the plurality of energy storage sub-systems so as to alternatively deliver electrical power to the electrical distribution network and absorb electrical power from the electrical distribution network. In this way, one can use the flywheel energy storage systems that have given up energy to the electrical distribution network as an energy sink for absorbing the excess electrical power being generated.

In yet further embodiments, the energy storage sub-system includes a plurality or more of flywheel energy storage systems and the methodology of the present invention includes separately operating each of the plurality of flywheel the energy storage systems so as to operate selective ones of the plurality of flywheel energy storage systems to deliver electrical energy to or absorb electrical energy from the electrical distribution network. For example, one or more of the plurality or more flywheel energy storage systems can be operated to deliver or absorb electrical energy and the other of the plurality or more flywheel energy storage systems can be operated in a free-spin or a standby operating mode, where energy is not being delivered or absorbed by the other flywheel energy storage systems.

In another aspect of the present invention, the energy storage sub-system comprises an adjustable load and the flywheel energy storage systems. In more particular embodiments, the frequency regulating methodology of the present invention includes configuring the plurality or more of flywheel energy storage systems and the adjustable load so that one or both of them absorbs electrical energy from the electrical distribution network. In this way, excess electrical energy being generated is temporarily absorbed by the one or more, or the plurality or more, flywheel energy storage systems of a given energy storage sub-system and/or provided to the adjustable load.

The adjustable load can comprise a sink or a soft load that can be relatively easily unloaded and re-loaded from the energy storage subsystem. For example, the sink or soft load could be a resistive heating element that is separately coupled to the distribution grid. Thus, the absorbed electrical energy is separately and controllably delivered to the resistive heating element so as to provide useable heat energy or heat energy that is dumped to a heat sink (e.g., atmosphere). In another example, the soft load is another device, apparatus or system such as a pump or chiller unit where the other device, apparatus or system can use the excess energy as useable electrically energy (e.g., make ice, pump a fluid). The adjustable load can be established so as to be capable of absorbing electrical energy equal to that capable of being absorbed by the flywheel energy storage systems or the pre-established maximum absorption capability for the energy storage sub-system. In more particular embodiments, the adjustable load is set so as to absorb an amount of energy equal to about 100% or less of the pre-established maximum absorption capability for the energy storage sub-system, more specifically about 50% 40%, 30%, 20% or 10% of the pre-established maximum absorption capability.

In further aspects of the present invention, the methodology of the present invention includes establishing a set point corresponding to a predetermined amount of electrical energy, the set point corresponding to a predetermined percentage of the maximum capability of the energy storage sub-system to absorb or provide electrical power. The predetermined percentage is about 20%, about 30% and being about 50% or less.

In further embodiments, the methodology of the present invention includes configuring the energy storage sub-system so that power delivery and absorption is determined based on the set point. In more particular embodiments, the methodology further includes absorbing power from the distribution network equal to the set point using the adjustable load.

In further embodiments, when delivering power to the distribution network the methodology includes diverting power from the adjustable load and delivering power equal to the set point to the distribution network and using power from the flywheel energy storage systems to meet additional power requirements. In further embodiments, when absorbing power from the distribution network, the methodology includes configuring the energy storage subsystem so as to absorb power from one or both of the adjustable load and the flywheel energy storage systems. In a more particular embodiment, the methodology includes evaluating the capacity of the flywheel energy storage systems to absorb energy and controlling the adjustable load to complement the capacity of the flywheel energy storage systems.

Other aspects and embodiments of the invention are discussed below.

BRIEF DESCRIPTION OF DRAWINGS

For a fuller understanding of the nature and desired objects of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawing figures wherein like reference character denote corresponding parts throughout the several views and wherein:

FIG. 1A is an exemplary daily load curve illustrating variation as a function of time of the electrical load;

FIG. 1B is an exemplary load curve illustrating short-term variation in the daily load illustrated in FIG. 1A between the hours of midnight and 3 AM;

FIG. 2 is an exemplary curve illustrating variation in AC frequency as a function of time over a 24 hour time period;

FIG. 3A is graph including generation and load curves for a fossil-fuel power generator with a varying load;

FIG. 3B is a graph including generation and load curves for a pumped Hydropower generator with to a varying load;

FIG. 3C illustrates an algorithm of one technique for determining area control error.

FIG. 4 is a block diagram of an exemplary power generation and distribution system illustrating various placements of an FESS array of the present invention;

FIG. 5 is a perspective view of an exemplary FESS array of the present invention;

FIG. 6 is a block diagram of an exemplary FESS array according to one aspect of the present invention with four FESS units;

FIG. 7A is a high level flow diagram illustrating a methodology according to an aspect of the present invention; and

FIG. 7B is a flow diagram illustrating a methodology according to the present invention for controlling the FESS array;

FIG. 8A is a schematic view of another embodiment of an FESS array according to the one aspect of the present invention;

FIG. 8B is a schematic view that more particularly illustrates the connection of the FESS array of FIG. 8A to the electrical distribution grid;

FIG. 9A is a high level flow diagram illustrating another methodology according to the present invention for controlling the FESS array of FIGS. 8A,B;

FIG. 9B is a continuation of the high level flow diagram of FIG. 9A.

FIG. 10 is a graphical view illustrating a regulation signal and set point;

FIG. 11 is a schematic view of an FESS array according to other aspects of the present invention;

FIG. 12A is a high level flow diagram illustrating another methodology of the present invention for controlling the FESS array of FIG. 10;

FIG. 12B is a continuation of the high level flow diagram of FIG. 12A.

FIG. 12C is a continuation of the high level flow diagram of FIG. 12A.

FIG. 13A is a schematic diagram of an array of a multiple of flywheel energy storage systems illustrating a master-slave arrangement;

FIG. 13B is a flow diagram illustrating a methodology according to the present invention whereby the FESS array controller controls output voltage;

FIG. 13C is a power regulation circuit under the control of a digital signal processor embodied in the FESS electronics module 122; and

FIG. 13D is a flow diagram of the applications program being executed in the digital signal processor of FIG. 9C.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the various figures of the drawing wherein like reference characters refer to like parts, there is shown in FIG. 4 a block diagram of an exemplary power generation and distribution system 10 coupled to any one of a number of system loads 18, 18′ (e.g., loads imposed by customers or users) and which illustrates various placements of an FESS array 100 of the present invention within such a system. The exemplary power generation and distribution system 10 includes one or more power generation facilities 12, 12′ that are selectively and electrically coupled to the power distribution grid 14 using any of a number of techniques known to those skilled in the art. Such power generation facilities 12, 12′ includes fixed sites, such as fixed fossil-fuel or nuclear power generation facilities, hydroelectric power generation facilities; battery farms; pumped hydro power generation facilities; diesel generators, or green (e.g., wind powered or solar powered) power generation facilities. The power generation facility 12, 12′ also can be configured so as to be generally mobile so as to be re-locatable and electrically coupled to any one of a node or point in a distribution system.

An FESS array(s) 100 according to the present invention can be located at any of a number of locations within the power generation and distribution system 10. In one illustrative embodiment, an FESS array 100 is located at or proximal a power generation facility 12′ and coupled to the distribution grid 14 at that location. In another illustrative embodiment, a FESS array sub-system 200 that includes a plurality or more of FESS arrays 100 is located in the power distribution grid 14 and is electrically coupled thereto. In another illustrative embodiment, an FESS array 100 is located at or proximal a node 16 or other connective point of a power distribution system that feeds one or more loads 18. In another illustrative embodiment, an FESS array 100 is located at or proximal the site of a load 18′ (e.g., a large manufacturing facility).

The foregoing is illustrative of a few general locations within the power generation and system 10 where an FESS array 100 or an FESS array sub-system 200 can be located. This shall not, however, be construed as limiting the FESS array 100 or the FESS array sub-system 200 to the illustrated locations as it is contemplated and within the scope of the present invention for the FESS array or FESS array sub-system to be located anywhere within a power generation and distribution system by which frequency regulation can be accomplished as taught herein. In use, the power generation and distribution system 10 is configured and arranged with one or more FESS arrays 100 or one or more FESS array sub-systems 200 having sufficient power capacity so as to effect regulation of the AC frequency of the power being transmitted in the system alone or in combination with other power generation facilities.

Referring now to FIG. 5, there is shown a perspective view of a partial cutaway of an exemplary FESS array 100 according to the present invention. In the illustrated embodiment, the FESS array 100 includes one or more flywheel energy storage system (FESS) units 120 as is known in the art, more particularly a plurality or more FESS units, and more specifically a multiplicity of FESS units. In the illustrated embodiment, the FESS array 100 is configured so the array of FESS units 120 can be enclosed in a housing 150 or structure. Such a housing 150 or structure provides a mechanism by which the FESS array 100 can be constructed at a remote location and then moved to the desired location for use instead of being constructed on-site. Also enclosed within the housing 150 are the cabinets or modules 125 of the electronics associated with the operation of the array, power conditioning and other systems (e.g., HVAC) related to operation of the array and/or the structure. This shall not be construed as limiting the present invention, as an FESS array 100 according to the present invention can be arranged on-site in a fixed configuration. In addition, it also is contemplated that an FESS array 100 of the present invention to be disposed within a mobile housing, for example a semi-tractor trailer unit (e.g., box), whereby the mobile housing can be moved from location to location by a motor vehicle such as a truck and/or a train.

It should be recognized that the number of FESS units 100 that make up a given FESS array is dependent upon a number of factors including, but not limited to, the total energy to be developed or delivered by the FESS array, the amount of energy that can be delivered per unit time by the FESS array, the time period such power is to be delivered by the FESS array, the total amount of energy that can be delivered by each FESS unit, the amount of energy that can be delivered per unit time by each FESS unit, whether the array is configured so as to be mobile (e.g., transportable) or a non-mobile design, and the room or space available at the site at which the FESS array is to be located.

In illustrative embodiments, FESS units 120 contemplated for use in an FESS array of the present invention each have electrical capacities ranging from about 1 kW to about 250 kW. It should not be construed that the electrical capacities of each FESS unit 120 is limited to the illustrative values, as the electrical capacity can be of any value including, but not limited to, 500 Kw or less or 500 Kw or more. In a particular exemplary illustrative embodiment, the FESS array 100 is configured and arranged so as to include 10 FESS units 120, where each FESS unit is capable of providing about 25 kWh of electrical energy. The so-configured FESS array 100 can provide about 1 MW of electrical power for 15 minutes or about 2.5 MW of electrical power for about 5 minutes. It also is contemplated and within the scope of the present invention for an FESS array 100 to be made up of FESS units 120 having different power producing capabilities.

In addition to controlling the number of FESS units 120 making up an FESS array 100, the present invention also contemplates locating an FESS array sub-system 200, made up of a plurality of more of FESS arrays, at a given location as is illustrated in FIG. 4. This shall not be construed as limiting an FESS array sub-system 200 to any specific number of FESS arrays 100, as a FESS array sub-system of the present invention is scalable so as to include any of a number of FESS arrays and thus scalable to provide any desired amount of power including an FESS array sub-system comprised of 40 FESS arrays at a given location. Using the above, exemplary illustrative embodiment, an FESS array sub-system 200 made up of 2 FESS arrays 100 can provide about 2 MW of electrical power for 15 minutes or about 5 MW of electrical power for about 5 minutes. It also is contemplated and within the scope of the present invention for an FESS array sub-system 200 to be made up of FESS arrays 100 having different configurations, such different number and power level types of FESS units 120, as well as FESS arrays 100 having different power producing capabilities. As indicated herein it also is within the scope of the present invention that the individual FESS units making up an FESS array 100 be controlled so as to provided or absorb power altogether or on an individual basis. As indicated herein it also is within the scope of the present invention that the individual FESS arrays 100 of an FESS array sub-system 200 be controlled so as to provided or absorb power altogether or separately.

Referring now to FIG. 6, there is shown is a block diagram of an exemplary FESS array 100 a with four FESS units 120 and an array controller 130. As indicated above, an FESS array according to the present invention can include one or more FESS units, a plurality or more of FESS units, a multiplicity or more of FESS units, four or more FESS units, 4 to 10 FESS units, 10 FESS units, or 10 or more FESS units, where the number of FESS units making up the FESS array is sufficient so the so-configured array should provide the desired power output for the desired amount of time and at the desired output voltage. As indicated herein, a number of such arrays 100 a can be ganged or arranged in a substation connected to a common AC bus so the combined array can output and/or absorb more electrical power than if a single array was provided. In addition, such multiple arrays also can be arranged as further 30 described herein so as to maintain the capability to absorb electrical energy and provide or inject electrical energy into the electrical distribution grid.

The FESS units 120 are any of a number of flywheel energy storage systems known to those skilled in the art, which are generally characterized by the ability of each flywheel energy storage system to store electrical energy in the form of kinetic energy typically by use of a rotating member and to convert the stored kinetic energy into electrical energy on demand. One conventional flywheel energy storage system, such as that described in U.S. Pat. No. 6,262,505 the teachings of which are incorporated herein by reference, includes an electronics module or flywheel controller 122, and a flywheel module 124. The flywheel module includes a flywheel/rotor assembly 126 and a motor/generator 128 that is mechanically coupled to the flywheel/rotor assembly. The flywheel module 120 constitutes the actual mechanical motor/generator system that is typically based on a permanent-magnet-brushless design and this electromechanical system is typically controlled and monitored by the flywheel controller 122. It is contemplated and thus within the scope of the present invention for the mechanical motor/generator system to comprise any of a number of other motor type designs including, but not limited to, reluctance motors and inductance motors. Such a flywheel energy storage system also is enclosed within a housing that is maintained under vacuum conditions so as to minimize retarding forces on the flywheel rotor assembly.

Such a flywheel energy storage system is generally operated in one of three major operating modes, a charging mode, a standby mode and a power generation or producing mode, however, other operating modes or states for regulation of frequency are contemplated and thus within the scope of the present invention as more particularly described hereinafter. In the charging mode, the flywheel controller 122 configures the motor/generator 128 so as to function as a motor and connects the motor/generator to a source of electrical power. The electrical power is used by the motor/generator/128 so as to spin the flywheel/rotor assembly such that the rotor or flywheel reaches a predetermined minimum rotational speed or a rotational speed that is in a desired range of rotational speeds. In this way, electrical power being delivered to the flywheel energy storage system is converted to kinetic energy. Upon reaching or attaining the predetermined initial rotational speed or a rotational speed in the desired range, the flywheel controller 122 disconnects the motor/generator from the source of electrical power.

After completion of charging, the flywheel is operated in a standby mode, where the flywheel/rotor assembly 126 is maintained in a generally continuing rotational state. The flywheel/rotor assembly 126 is typically enclosed within a housing (not shown) that is maintained under vacuum conditions and the rotor/flywheel utilize bearings that are generally characterized as being frictionless or having minimally frictional effect. In this way, retarding forces that could act on the flywheel/rotor of the flywheel/rotor assembly when in the standby mode are thereby minimized.

After an FESS unit 120 is put into its initial operating (i.e., spinning) state, the flywheel controller 122 monitors the operational condition of the FESS unit, including the rotational speed of the rotor/flywheel. When the rotational speed of the rotor/flywheel drops below a predetermined value, the flywheel controller 122 reconnects or recouples the motor/generator 128 to the source of electrical power, while the motor/generator 128 is configured to function as a motor. In this way, the rotational speed of the rotor/flywheel of the flywheel/rotor assembly 126 can be increased and after again reaching the predetermined desired rotational speed or being with the desired range of rotational speeds, the electronics module 122 disconnects the motor/generator from the electrical power source. In this way, the flywheel controller 122 automatically maintains the power producing capacity of the FESS unit so as to be in a desired range when in the standby mode.

It should be noted that the foregoing is one of the auxiliary loads that would be associated with normal operation of the of the array 100 a of FESS units 120. Such other loads including power for the flywheel controller 122, lubricating and cooling systems for the FESS units, and heating and cooling systems (HV AC systems for the housing 150 or structure containing the FESS units 120 as well as any other associated control and power conversion electronics obtain power from the electrical distribution grid in any of a number of ways known to those skilled in the art and as such are not specifically detailed further here in regards to FIG. 6.

When the FESS unit is to produce power, the flywheel controller 122 configures the motor/generator 128 so as to function as a generator. Because the motor/generator 128 is mechanically coupled to the flywheel or rotor of the flywheel/rotor assembly 126, the motor/generator uses the rotational kinetic energy provided by the spinning rotor/flywheel to generate electrical energy. Typically, the flywheel controller 122 also would electrically couple the motor/generator 126 to the electrical load.

As described in U.S. Pat. No. 6,262,505, the flywheel controller 122 also is configurable so as to monitor a number of operational parameters and providing localized control over the operation of the FESS unit. In particular embodiments, the flywheel controller 122 monitors operational parameters to determine if the rotation of the flywheel/rotor of the flywheel/rotor assembly should be terminated or reduced, such as in the case of a detected over speed condition or where there are indications suggesting of possible rotational instability or potential failure of the flywheel/rotor assembly. If the flywheel controller 122 determines that action should be taken, the flywheel controller causes the FESS unit to shutdown (e.g., stop the rotor/flywheel from spinning) and typically outputs a signal indicating such shutdown.

In addition, and as described in U.S. Pat. No. 6,262,505, the flywheel controller 122 also is configured and includes mechanisms by which such operating parameters and/or operational status also are outputable to a remote monitoring location, such as a control room remote from the FESS unit 120, so as to allow operational condition or performance of the FESS unit to be remotely monitored and thus providing information relative to FESS unit availability and capability. In the present invention, such monitoring/reporting signals are sent from each FESS unit 120 of the FESS array 100 to the array controller 130. The array controller 130 accumulates these signal and communicates such signals to the remotely located monitor 140. Alternatively, it is contemplated that such monitoring and reporting is accomplished by sending the monitoring/reporting signals from each FESS unit 120 of an FESS array to the remotely located monitor 140.

The array controller 130 includes a CPU 132, having a memory and storage 134. As described herein, the present invention also includes one or more applications programs for execution in the CPU 132. The array controller 130, more particularly the applications programs being executed, is configured and arranged so as to control communications between a dispatch location 150, and/or between the remotely located monitor 140 and the array controller 130 as well as between and among the FESS units 120 comprising the FESS array 100. The array controller 130, more particularly the applications programs being executed therein, also is configured and arranged so as to control the operation of the one or more FESS units 120 of the array so as to deliver electrical power to the power distribution system or to absorb electrical power form the electrical distribution systems responsive to signals from the dispatch location 150 such as the regulation signals illustrated in FIG. 10.

The storage 134 for the array controller 130 is any of a number of volatile or non-volatile storage mechanisms or memories known to those skilled in the art that are appropriate for the intended use. Such non-volatile storage mediums include flash or spindle types of memory including for example NVRAM as well as hard drives. In addition, such storage 134 can comprise different forms of storage media such as flash and spindle types of memory. The storage 134 can be used for storing information and/or the one or more applications programs. In more particular embodiments, the storage 134 temporarily stores operating conditions/parameters for each of the FESS units 120 of the FESS array. In this way, the CPU 132 can perform a routine periodic batch transmission of such operating conditions/parameters to the remote monitor 140 as well as transmitting such information at other times when appropriate. The CPU 132 and the associated memory, include any of a number of devices known to those skilled in that art that are appropriate for the intended use and application.

The FESS array 100 also includes a switching mechanism 160 that couples and de-couples the FESS array from the electrical distribution system. The switching mechanism 160 is any of a number or switches or switching circuitry known to those skilled in the art appropriate for the intended use. Alternatively, the FESS array 100 is configured and arranged with a plurality of switching mechanism 160, where a switching mechanism is located in the line from each FESS unit 120 coupling the FESS unit to the electrical distribution network. In further embodiments, a switching mechanism 160 also is located in the common line to the electrical distribution network as illustrated in FIG. 6.

Although a single line between each of the FESS units 120 and the electrical distribution network is illustrated, this shall not be limiting as a plurality or more lines can be provided between the distribution network and FEES unit. For example, a power input line is provided to each FESS unit 120 for delivering electrical power to the FESS unit and an output line is provided to each FESS unit to deliver electrical power from the FESS unit to the electrical power distribution system.

The operation of an FESS array 100 or an FESS array sub-system 200 and the methodology embodied in the one or more applications programs for execution within the array controller 130 can be best understood from the following discussion with reference to the flow diagram illustrated in FIGS. 7A,B. In addition, reference also shall be made to FIGS. 4-6 and the related discussion for details regarding the functional components of the FESS array 100 or the FESS array sub-system 200 not otherwise provided in the following discussion.

Referring now to FIG. 7A, there is shown a high level flow diagram illustrating a methodology according to one aspect of the present invention for regulating frequency using one or more FESS arrays 100. Initially the user or power-generating supplier configures each of the one or more FESS arrays 100 to provide the desired power generating capacity, STEP 500.

As indicated herein, the FESS array 100 according to the present invention is composed of one or more FESS units 120, where each FESS unit is configured and arranged so as to have a predeterminable power generating capacity when the flywheel/rotor of the flywheel/rotor assembly 126 is being rotated in the predetermined range of rotational speeds. As such, an FESS array 100 of the present invention is thus scalable to provide different power generating capacities by appropriately configuring a given FESS array with the number of FESS units required to attain the desired power generating capacity. For example, to yield an FESS array 100 with a desired power generating capacity of 1-2.5 MW for 15-5 minutes, then one could configure the array so as to be composed of 10 FESS units 120 capable of producing 25 kWh (5 Kw). If additional capacity is required for example, lets say providing power generating capacity of 3-7.5 MW for 15-5 minutes, then one would scale up the FESS array 100 so as to include more FESS units 120.

Alternatively, a user or power-generating supplier would provide a plurality or more of FESS arrays 100 that are combined to form an FESS array sub-system 200. In such a case, each of the FESS arrays 100 would be configured with a power generating capacity that when combined in the aggregate would yield an FESS array sub-system 200 having the desired power generating capacity. For ease of use, a power-generating supplier can pre-configure an FESS array 100 so as to have a set power generating capacity for a given time period and to scale up to the required capacity by supplying a plurality or more of such FESS arrays 100. Such a configuration for an FESS array sub-system 200 also yields a configuration, whereby the addition, deletion or absorption of electrical power can be further controlled by controlling how many of the FESS arrays 100 of a given sub-system are electrically coupled to the electrical distribution network.

It should be recognized that such configuring also takes into account whether the one or more FESS arrays 100 are to be fixed sites or sites composed of FESS arrays that are transportable or mobile. In the case of transportable or mobile arrays, the scalability of an FESS array is subject to the limitations imposed by the means or mechanisms by which the FESS array is being transported. For example, a truck distributed FESS array would be subject to width and length restrictions imposed on vehicles using the highways. Such configuring also would consider how many of the one or more FESS arrays 100 are to be distributed within an electrical power distribution network and the requirements or limitations imposed at the physical location where the each of the one or more FESS arrays are to be located.

Each of the one or more FESS arrays also is configured with the control circuitry necessary for controlling the operation of the one or more arrays so the one or more arrays are selectively coupled or decoupled from the power distribution network and when coupled to provide power (e.g., inject power) to, or absorb power from, the power distribution network. The foregoing are illustrative of a number of the considerations that a power-generating supplier would evaluate or consider when configuring an FESS array, however, the foregoing shall not be considered as limiting the present invention only to these considerations and/or situations.

After configuring the one or more FESS arrays 100 for use in an electrical distribution network, the power-generating supplier operably couples the one or more FESS arrays 100 and/or the one or more FESS array sub-systems 200 to the electrical distribution network, step 502 such that the FESS arrays/FESS sub-systems are electrically coupled to the power distribution network. As illustrated in FIG. 6, it is within the scope of the present invention, to position one or more switching mechanisms 160 so the FESS array 100 and/or the FESS units 120 of the array can be electrically coupled to the distribution network.

After operably coupling the one or more FESS arrays 100 and/or the one or more FESS array sub-systems 200 to the distribution network, the power-generating supplier electrically initializes each FESS array or each FESS array sub-system so as to be capable of providing electrical power to the power distribution network, STEP 504. Such initializing is accomplished by electrically coupling each FESS array 100 and/or each of the FESS units 120 of the FESS array to the power distribution network and putting each of the FESS units into its charging mode so as to draw power from the power distribution network, as herein described. In this way, the power drawn from the power distribution network is converted into kinetic energy and this kinetic energy is stored within the FEES unit 120 as herein described and as is known to those skilled in the art. It is contemplated, and within the scope of the present invention, for the FESS arrays to be controlled such that such initializing occurs at times when it is determined that there is excess generating capacity in the distribution network and that this excess energy can be absorbed by a given FESS array 100. In this way, excess power can be stored and re-distributed back to the distribution network at a later time.

After initializing the one or more FESS arrays 100 and/or FESS array subsystems 200, the operation of the FESS arrays/FESS array sub-systems is controlled by the operational needs and circumstances of the electrical power distribution network. This is accomplished by first making a periodic determination each time after a predetermined time period has elapsed, STEPS 506, 508. According to one known techniques, the owner or agent of a power distribution network or the agent of the owners of a plurality or more of power distribution networks, basically makes a periodic comparison (e.g., once every two (2) or four (4) seconds) of the total power being generated and the electrical load on the network and determines what the difference is between the generated power and electrical consumption (i.e., lines losses for the transmission and distribution network and customer load(s)) at that time and also what this difference will be for some time in the near future.

Typically the “some time” in the future is established based on the time required for a given power/frequency regulation power generating facility to react (e.g., add or reduce power generating capacity). With existing or conventional power generating facilities, such reaction time periods vary based on the type of power generating facility, however, the present rule of thumb for those power generating facilities that are used for fine tune regulation (i.e., fine tune regulation of frequency) is a reaction time of about five (5) minutes. It should be recognized, that FESS units 120 advantageously are capable of being loaded and unloaded from the power distribution network with greater speed that such conventional power generating facilities without creating an operational detriment to the FESS units as compared for example, to the harm such cyclical loading/unloading can create for the batteries of a battery farm. As is known to those skilled in the art, the determination as to the future difference between the power generation and electrical power consumption also can take a number of other consideration into consideration to yield a correction error signal.

A further determination is made based on the correction signal being outputted as to what action should be taken to adjust the power being generated and being delivered to the power distribution network, Step 510. If it is determined that the power being generated matches the load (YES, Step 510), then the process returns to initiating or performing the above determination process after the next time period has elapsed. It is more likely, however, given the manner in which the power consumption (customer load plus network/line losses) can vary as a function of time, 25 that such a determination determines that there is and will be a mismatch (NO, Step 510) because too little or too much power is being generated as compared to power consumption. Thus, the agent or dispatcher outputs correction signals to each of the power generating facilities used for power and frequency regulation, Step 512. There is shown in FIG. 10 a graphical view that illustrates a typical regulation signal output as a function of time that generally comprises the correction signal outputted by the dispatcher/agent.

For an electrical power distribution network that include one or more FESS arrays 100 and/or one or more FESS array sub-systems 200, the FESS arrays/FESS array sub-systems evaluate such correction signals to determine if it is a signal for modifying the operation of a given FESS array/FESS array sub-system, Step 514. In cases where the correction signal is not being outputted to a given FESS array/FESS array sub-system (NO, Step 514) then the process continues as with conventional techniques for regulation, whereby power generating capacity is added or deleted and/or the control signal is used to adjust (i.e., increase or decrease) the power generating capacity of a given power generating facility.

If it is determined that the power generating correction signal is for a given FESS array 100 or FESS array sub-system 200 (YES, Step 514), then the FESS array is controlled so as to alter the present operational status and condition of the FESS array or FESS array sub-system, Step 516. More particularly, the array/array subsystem 100/200 is controlled so as to adjust the power being delivered, so as to increase or decrease the amount being presently delivered; by altering the FESS unit operating mode from power delivery or power production to the charging mode so as to absorb excess power being generated; or by putting the FESS units in a standby mode so as to in effect remove or delete this power generating capacity from the power generation network.

It should be recognized that in addition to the timely responsiveness of an FESS array, in contrast to known and existing techniques and power generating facilities, an FESS array/FESS array sub-system 100/200 also can be advantageously configured to absorb electrical power. Thus, and in contrast to conventional techniques, the power being generated by other power generating facilities need not be automatically adjusted (e.g., decreased) or dropped to fine tune and match the total load of the system over the short time period of the mismatch as such fine tuning is accomplished by the FESS array/FESS array sub-system. Moreover, it is contemplated that the methodology, devices and systems of the present are adaptable so such absorbing of power is coordinated so that an FESS array 100 that has delivered power to the network is the array that is later selected for absorbing power from the network. In this way, the excess power is in effect stored in the FESS array for later delivery to the distribution network.

Referring now also to FIG. 7B there is shown a flow diagram illustrating a methodology according to the present invention for controlling an FESS array 100, and more particularly the methodology embodied in the one or more applications programs for execution within the array controller 130. After the FESS 100 array has been configured, operably coupled to the power distribution network, and initialized (FIG. 7A, Steps 502-506), the process for controlling operation of the FESS array 100 and each of the FESS units 120 making up the FESS array is started, STEP 600. It should be recognized that it is contemplated in the present invention that the flywheel controller 122 of a given FESS unit 120 provides local control over the operation of the corresponding FESS unit as well as monitoring operational parameters and the like of the corresponding FESS unit. It also is within the scope of the present invention, for the FESS array controller 130 to also be configured and arranged so as to be capable of replicating and/or performing one or more of the control and/or monitoring functions of the flywheel controller 122.

After starting, the FESS array controller 130 monitors the communications link or network the FESS array is operably coupled to, for power correction signals from the remote dispatch 150 or control location, Step 602. When such control signals are received, the FESS array controller 130 then determines the operational configuration of the FESS array 100 and for each of the FESS units 120 thereof, Step 604. The array controller 130, responsive to such a determination, outputs the appropriate control signals to the FESS units 120 of the array so the array is in the determined operational configuration, Steps 606, 608.

Thus, if power is being delivered to the power distribution network for purposes of regulating the AC frequency of the power distribution network, the FESS array controller 130 outputs signals to each of the FESS units 120 of the array causing the flywheel controller 122 of each FESS unit to configure the motor/generator 126 as a generator. Alternatively, if power is to be absorbed then the FESS array controller 130 outputs signals to each of the FESS units 120 of the array causing the flywheel controller 122 of each FESS unit to configure the motor/generator 126 as a motor. Also, if the present absorption or delivery of power is to be terminated, the FESS array controller outputs signals to terminate such actions, for example, by having the flywheel controller 122 put the FESS unit 120 in the standby mode, or alternatively by locally de-coupling the FESS unit from the power distribution network. Although, it is expected that the FESS units 120 of the FESS array 100 will be operated in a unitary fashion, the present invention also contemplates having the FESS array controller 130 configured and arranged so it controls the FESS units individually such that one or more FESS units of a given FESS array can be operated differently than other FESS units of the array.

In the case where the FESS units 120 of the FESS array 100 are being put into the standby mode or status {YES, Step 610), then the process returns to monitoring the communications link for power correction/regulation signals. If the FESS array 100 is configured so as to deliver or absorb power then the FESS array controller 130 monitors the performance of the array to determine if the array configuration is operating as intended, Steps 612, 614. If it is determined that the FESS array configuration is not performing as intended (No, Step 614), then the process returns to determining the configuration of the array 100 and repeats the foregoing. Essentially, the FESS array controller 130 re-evaluates the configuration of the array 100 to determine another configuration for the array. If it is determined that the FESS array configuration is performing as intended (YES, Step 614), then the process returns to monitoring the communications link for power correction/regulation signals (Step 602).

As indicated herein, the flywheel controller 122 of each FESS unit 120 typically monitors operational parameters and/or characteristics and provides output signals representative of monitored parameters/characteristics. In a further embodiment, the FESS array controller 130 is configured and arranged so as to monitor communication links with each of the FESS units 120 of the FESS array 100 for such monitoring/reporting signals from an FESS unit, Step 630. After receiving such signals, the FESS array controller 130 communicates the received signals to a remotely located monitoring site 140, Step 632. It also is contemplated that such signals to be outputted to an apparatus or device (e.g., laptop computer) that is electrically coupled to the array controller 130, for example via a RS-232 port or other communications interface as is known to those skilled in the art.

In particular embodiments, the array controller 130 is configured and arranged so as to receive and store such signals from all of the FESS units 120 of the FESS array 100 in the array controller storage 134. The FESS array controller 130 also is configured and arranged so as to communicate such stored information to the remotely located monitoring site 140 at one or more predetermined times, typically periodically. For example, communicating such information at particular times when the communications load on the communication links/networks is expected to be or typically is reduced. In more specific embodiments, the FESS array controller is configured and arranged so as to perform an evaluation of certain parameters or characteristics and in cases where the parameters or characteristics of a particular FESS unit 120 are outside an established value or exhibit a particular trend, the FESS array controller communicate the monitored parameters/characteristics to the remotely located monitoring site 140, with or without a flag or other indicator representative of a potential out-of norm condition.

Referring now to FIG. 8A, there is shown a schematic view of another embodiment of an FESS array 100 b according to the present invention. Reference shall be made to the foregoing discussion for the FESS array 100 a of FIG. 6 for the details and arrangements for any features or elements having common reference numerals. The FESS array 100 h according to this embodiment differs from that shown in FIG. 6 in that the motor/generator 128 b of this embodiment is configured and arranged so the FESS unit 120 b provides a DC output (e.g., a 700 volt DC output). In the FESS array 100 a of FIG. 6, each of individual FESS units 120 provides an AC output.

As such, each FESS unit 120 further includes a bi-directional inverter 129, as is known to those skilled in the art. The bi-directional inverter 129 of each FESS unit is operably and electrically coupled to a DC bus 170. The bi-directional inverter 129 is configured and arranged so as to convert AC outputs from the flywheel motor/generator 126, when it is being operated as a generator, to a DC output. When the flywheel motor/generator 126 is being operated as a motor to charge the FESS unit, the bi-directional inverter 129 converts the DC voltage and current on the DC bus 170 to an AC output.

The DC outputs from each of the FESS units 120 are inputted to the DC bus 170 (e.g., a common DC bus) that includes DC switchgear. The DC bus 170 is any of a number of electrical circuits and materials as is known to those skilled in the art for conducting the DC current and voltage outputs to the power conditioning module 172. The power-conditioning module is any of a number of bi-directional inverters known to those in the art for converting a DC output from the array of flywheel energy storage systems to a desired AC output and for correspondingly converting an AC input to a DC output, when charging the FESS units 120. In an illustrative embodiment, the power-converting module 172 converts a 700-volt DC input to a 10 480-volt AC output, more specifically a 480-volt three phase AC output. In an illustrative exemplary embodiment, the power-conversion module 172 includes IGBT power electronics and is controlled by a DSP/FPGA-based, high-speed digital controller.

As indicated herein, there are a number of auxiliary components associated with each flywheel unit 120, the power conditioning module 172, the array controller 130 and other components associated with the housing 150 that receive electrical power from the electrical distribution grid. These auxiliary loads are illustrated schematically as the feature entitled system ancillary loads 182.

Referring now also to FIG. 8B there is shown another schematic view that more particularly illustrates the electrical connection between the FESS array 100 b and the grid interface 15 or grid interconnection with the electrical distribution grid. Since the voltage level of the electrical grid interface 15 is typically connected to an electrical distribution line that is operating a higher voltage level (e.g., 35, 69, 115 KV) than the AC voltage output from the power conversion module 172, the FESS array 100 b further includes a step-transformer 174 that is operably, electrically coupled to the grid interface 15 and the power conditioning module 172. The step-up transformer 174 is any of a number of transformers known to those skilled in the art and that are appropriate for the intended use and operating conditions. Although this is being illustrated with reference to the FESS array of FIG. 8A, it is contemplated and within the scope of the present invention for such a step-up transformer to be used with the FESS array 100 a shown in FIG. 6.

The operation of the FESS array 100 b is understood when reference is taken to the foregoing discussion of FIG. 7A as well as to FIG. 8A, FIGS. 9A,B and the following discussion. In this regard, reference shall be made to the foregoing discussion for FIGS. 8A,B and FIG. 6 for details and features of the array not otherwise include in the following. Reference shall be made to the foregoing discussion of FIG. 7A, that generally describes the process of locating an FESS array, configuring the array for use and the general process associated with absorbing power, providing power, and the stand by mode. The discussion which follows regarding FIGS. 9A,B relates to the specific process ort methodology being implemented in the array controller 130 to control the operation of the FESS array in general and the FESS units in particular. Reference shall be made to the discussion for FIG. 7B for those method steps shown in FIGS. 9A,B having the same reference numerals unless otherwise discussed below.

The array controller 130 continually monitors for correction signals, Step 602 such as the regulation signals shown in FIG. 10. In general, the regulation signal is representative of the amount of regulation that is requested to be provided over the next time step. The value being provided is between (−) 100% and (+) 100% of the maximum amount of power that can be provided/injected by the FESS array 100 b or the maximum amount of power that can be absorbed by the FESS array. The minus sign represent signals where power is to be absorbed from the grid and positive signals represent signals where power is to be delivered to the grid. It should be understood that in respect to the present invention the maximum amount is similar to a rated capacity of the FESS to deliver or absorb power and is not necessarily an indication of what the FESS array 100 b is actually capable of doing when it receives the regulation signal.

In more particular embodiments, the amount of power being injected or absorbed is typically measured downstream of the power conditioning module 172 and upstream of the step-up transformer 174. As indicated herein, the regulation signal is periodically updated by the system operator or agent and in more illustrative embodiments; the regulation signal is updated about every 2-4 seconds. As also shown in FIG. 10, when the FESS array is operated so as to have a non-zero base point or set point, the regulation signal refers to the amount of power being delivered/injected or absorbed with respect to the base or set point.

In the case of a set point, the set point as shown in FIG. 10 corresponds to the nominal power level of power being removed from the grid by the FESS array. The set point typically is a percentage of the full regulation signal or value. The set point is generally established with the power supplier/producer so as to be a constant value over an agreed period of time, such as for example one to 24 hours.

Once a correction or regulation signal is received, a determination is made to see of the value of the RS signal (hereinafter RS) is greater than zero, Step 620. Alternatively, the process could be set so that a determination is made to see if RS less than zero. Along with evaluating the relative value of the regulation signal, the array controller also acquire system information, STEP 622, that provides an indication of the status and capabilities of the FESS array. For example, information is obtained that provides an indication as to whether the FESS array can absorb or provide power and the amount of power that can be absorbed or delivered.

If it is determined that RS is greater than zero (YES, step 620), then the regulation signal is requesting that the FESS array 100 b provide or inject power of a specified amount to the grid. As such, the array controller 130 determines from the acquired system data if the FESS array 100 b has sufficient capacity to deliver power to the grid, STEP 624. If it is determined that the FESS array has sufficient capacity (YES, step 624) then the array controller 130 causes the FESS units 120 and FESS array to be configured so as to output power to the grid. In further embodiments, the array controller 130 is configured so as to include a minimum level that is used to determine if the actual capacity of the FESS array is sufficient. After configuring the array so that power can be outputted the process returns to monitoring for signals/messages to the FESS array.

If it is determined that the FESS array does not have sufficient capacity (NO, step 624) then the array controller 130 takes no further action and the process returns to monitoring for signals/messages to the FESS array. The minimum level is generally established so that the kinetic energy being stored in the flywheel is not below a predetermined value before outputting power or that the kinetic energy does not fall below the predetermined value following delivery of power.

If it is determined that RS is less than zero, (NO, step 620), then the regulation signal is requesting that the FESS array 100 b absorb generated power of a specified amount from the grid. As such, the array controller 130 determines from the acquired system data if the FESS array is fully charged, step 660 or alternatively a determination is made to determine if the FESS array has sufficient capacity to absorb power from the grid. If it is determined that the FESS array is fully charged (YES, step 660) indicating that the array cannot absorb energy, then the process returns to monitoring for signals/messages to the FESS array (Step 600, FIG. 9A). If it is determined that the FESS array is not fully charged (NO, step 660) then the array controller 130 causes the FESS units 120 and FESS array to be configured so as absorb power from the grid. In the present embodiment, the FESS units 120 are arranged so as to receive electrical energy from the grid and so as to increase the kinetic energy being stored in each FESS unit. After configuring the array so that power can be absorbed the process returns to monitoring for signals/messages to the FESS array, step 600, FIG. 9A.

Referring now to FIG. 11, there is shown a schematic view of an FESS array 100 c according to other aspects of the present invention. Reference shall be made to 20 the foregoing discussion for the FESS arrays 100 a,b of FIGS. 6 and 8A,B for the details and arrangements for any features or elements having common reference numerals. The FESS array 100 c according to this embodiment differs from the array shown in FIG. 8A, in that FESS array 100 c is configured and arranged so as to include an adjustable load 180.

The adjustable load 180 comprises a sink such as a load bank or a soft load that can be relatively easily unloaded and re-loaded from the FESS array 100 c. For example, the sink or soft load could be a resistive heating element that is separately coupled to the grid interface 15. Thus, the absorbed electrical energy is separately and controllably delivered to the resistive heating element so as to provide useable heat energy or heat energy that is dumped to a beat sink (e.g., atmosphere). In another example, the soft load is another device, apparatus or system such as a pump or chiller unit or desalinizer where the other device, apparatus or system can use the excess energy as useable electrically energy (e.g., make ice or salt, purify water, pump a fluid, etc.). The adjustable load can be established so as to be capable of absorbing electrical energy equal to that capable of being absorbed by the flywheel energy storage systems or the pre-established maximum absorption capability for the energy storage sub-system (i.e., 100% regulation signal value). In more particular embodiments, the adjustable load is set so as to absorb an amount of energy equal to about 50% the pre-established maximum absorption capability for the energy storage sub-system, more specifically about 40%, 30%, 20% Or 10%.

The operation of the FESS array 100 c of FIG. 11 is understood when reference is taken to the foregoing discussion of FIGS. 7A, 8A, 9A,B and FIG. 11 as well as to FIGS. 12A-C and the following discussion. In this regard, reference shall be made to the foregoing discussion for the circuitry of FIGS. 6, 8A,B and FIG. 11 for details and features of the array not otherwise included below. Reference also shall be made to the foregoing discussion of FIG. 7 A, that generally describes the process of locating an FESS array, configuring the array for use and the general process associated with absorbing power, providing power, and the stand by mode as well as the discussion of the controller controlling methodology of FIGS. 9A,b. The discussion which follows regarding FIGS. 12A-C relates to the specific process ort methodology being implemented in the array controller 130 to control the operation of the FESS array in general and the FESS units in particular. Reference shall be made to the discussion for FIGS. 7B and 9A,b for those method steps shown in FIGS. 12A-C having the same reference numerals unless otherwise discussed below.

The array controller 130 continually monitors for correction signals, Step 602 such as the regulation signals shown in FIG. 10. In general, the regulation signal is representative of the amount of regulation that is being requested to be provided by the FESS array 100 c over the next time step. The value being provided is between (−) 100% and (+) 100% of the maximum amount of power that can be provided/injected by the FESS array 100 b or the maximum amount of power that can be absorbed by the FESS array, where the minus sign represent power absorption and positive signals represent power to be delivered to the grid.

As also indicated herein and with reference to FIG. 10, when the FESS array is operated so as to have a non-zero base point or set point, the regulation signal refers to the amount of power being delivered/injected or absorbed with respect to the base or set point. In more particular embodiments, the set point is one or more parameters that is stored within the FESS array (e.g., in the array controller storage 134). The parameter(s) can be stored when the FESS array 100 c is initially configured or can be updated at a later time either locally or from a remote location. Alternatively, the set point can be a parameter that is sent by the system operator or agent who also sends out the regulation signals.

Once a correction or regulation signal is received, a determination is made to see of the value of the RS signal (hereinafter RS) is greater than zero, Step 620. Alternatively, the process could be set so that a determination is made to see if RS less than zero. Along with evaluating the relative value of the regulation signal, the array controller 130 also acquires system information, STEP 622 that provides an indication of the status and capabilities of the FESS array.

If it is determined that RS is greater than zero (YES, step 620), then an evaluation is made to determine if RS is larger than the auxiliary power level (AP), step 700 (FIG. 12B). If RS is greater than AP than the array controller 130 determines from the acquired system data if the FESS array 100 b has sufficient capacity at RS-AP to deliver power to the grid, Step 710. If it is determined that the FESS array has sufficient capacity (YES, step 710) then the array controller 130 causes the FESS units 120 and FESS array 100 c to be configured so as to output power to the grid. In more particular embodiments, the FESS array 100 c is configured so that the FESS units output a power output equal to about RS-AP. If the power equal to the set point (SP) being received by the FESS array is distributed to the adjustable load 180, then all or part of the power to the adjustable load also is diverted from the adjustable load back to the distribution grid.

If the FESS units do not have sufficient energy (NO, step 710) and the power equal to SP being received by the FESS array is distributed to the adjustable load 180, then the array controller 130 configures the FESS array 100 c so that the power to the adjustable load is diverted from the adjustable load back to the distribution grid, Step 711. The array controller 130 does not change operational status of the FESS units 120. After such configuring of the arrays, steps 711, 712, so that power can be delivered the process returns to monitoring for signals/messages to the FESS array, step 600, FIG. 12A.

If on the other hand RS is determined to be less than SP than the array controller 130 determines from the acquired system data if the FESS array 100 b is fully charged, step 720. If it is determined that the FESS array is fully charged with kinetic energy (YES, step 720) then the array controller 130 causes the FESS array 100 c to be configured so as to output power to the grid, Step 722. In more particular embodiments, the FESS array 100 c is configured so that the FESS units do not provide a power output and so the adjustable load is configured such that power equal to about actual power AP-RS is diverted from the adjustable load back to the distribution grid.

If it is determined that the FESS array is fully charged with kinetic energy (NO, step 720) then the array controller 130 calculates NP, which is the amount of power needed to charge the flywheel to full in the allocated time step, step 724. Thereafter the array controller 130 determines if NP is greater than AP-RS, step 730.

If it is determined that the NP is greater than AP-RS (YES, step 730) then the array controller 130 causes the FESS array 100 c to be configured so as to output power to the grid, Step 732. In more particular embodiments, the FESS array 100 c is configured so that the FESS units absorb power from the grid at a power level equal to about AP-RS and so the adjustable load 180 is configured so that the power is diverted from the adjustable load to charge the FESS units 120. Since the amount of power being taken off the grid is now the auxiliary power level less the regulation signal, this power is available for charging of the FESS units 120.

If it is determined that the NP is not greater than AP-RS (NO, step 730) then the array controller 130 causes the FESS array 100 c to be configured so as to output power to the grid, Step 734. In more particular embodiments, the FESS array 100 c is configured so that the FESS units absorb power from the grid at a power level equal to about NP and so the adjustable load 180 is configured so part of the power is diverted from the adjustable load to charge the FESS units 120 and so an output of about AP-RS-SP is outputted to the grid. After so configuring the array (steps 732, 734) the process returns to monitoring for signals/messages to the FESS array, step 600, FIG. 12A.

If it is determined that RS is not greater than zero (NO, step 620), then an evaluation is made by the array controller 130 determines from the acquired system data if the FESS array 100 c has sufficient capacity at absorb the excess power=abs(RS), Step 800. If it is determined that the FESS array has sufficient capacity to absorb the power, (YES, step 800 then the array controller 130 causes the FESS units 120 and FESS array 100 c to be configured so the FESS units 120 absorb energy and the adjustable load is set to absorb a load equal to AP, Step 804. If it is determined that the FESS array does not have sufficient capacity to absorb the power (NO, step 800 then the array controller 130 causes the FESS array 100 c to be configured so the FESS units do not absorb energy and so the adjustable load 180 is set to absorb a load equal to AP+abs(RS), Step 802. After so configuring the array (steps 802, 804) the process returns to monitoring for signals/messages to the FESS array, step 600, FIG. 12A.

According to another aspect of the present invention, each of the FESS arrays 100 are configured and arranged in any one of a number of fashions to control the output voltage of each of the FESS units 120 making up the array so as to assure power production from all the power producing FESS units of the array. There are shown in FIGS. 13A-D various techniques and/or circuitry for controlling the output voltage of each FEES unit.

Referring now to FIG. 13A, there is shown a schematic diagram of an array of a multiple flywheel energy storage system illustrating a conventional master-slave arrangement. In a conventional master-slave arrangement, one of the FESS units is designated the master and to determine the output voltage for all of the FESS units. The other FESS units are slaved to (i.e., controlled by) the master so their output voltage is controlled to voltage determined by the master. Reference shall be made to the discussion regarding FIGS. 1-2 of U.S. Ser. No. 09/998,122 (now allowed), the teachings of which are incorporated herein by reference as to further details regarding the functions and general design of the master-slave arrangement.

Referring now to FIG. 13B there is shown a flow diagram illustrating a methodology according to the present invention whereby the FESS array controller 130 controls the output voltage. When the FESS array 100, more particularly the FESS units 120 of the array, are configured to produce power and deliver same to the electrical power distribution network (YES, Step 900), the FESS array controller 130 monitors the output voltage of each of the FESS units, Step 904. This can be accomplished for example, by using the output voltage operational parameter being outputted by the flywheel controller 122.

The output voltage of each FESS unit 120 is evaluated to determine if the output voltages of the FESS units are synchronized or essentially the same. If the voltages are not synchronized, then the array controller 130 determines the appropriate corrected voltage that should be outputted, much like that is done by the master in the master-slave type of arrangement, and the FESS array controller 130 then outputs a signal to each of the FESS units requiring correction, STEP 908. The electronics module 122 of each of the affected FESS units 120 adjusts the operation of the motor/generator 126 responsive to the signal from the controller 130 so that the FESS unit is providing an output voltage at the desired value. In an exemplary embodiment, the FESS array controller 130 determines such a voltage adjustment using one of a predetermined value or by controlling the voltage to correspond to the lowest output voltage for an FESS unit. If the FESS array 100 is not delivering power or the voltages of the FESS units are determined to be synchronized, then the process is ended 902.

Referring now to FIGS. 13C, D there is shown a power regulation circuit under the control of a digital signal processor embodied in the FESS flywheel controller 122 (FIG. 13C) and a flow diagram of the applications program being executed in the digital signal processor (FIG. 9D). Reference shall be made to the discussion regarding FIGS. 3-7 of U.S. Ser. No. 09/998,122 (now allowed) and assigned to the assignee of the present invention, the teaching of which are incorporated herein by reference in their entirety, as to further details regarding the functions and design of the power regulation circuit, alternate embodiments thereof and the flow diagram.

In further aspects of the present invention, the FESS array 100 including the FESS units 120 and the array controller 130 are configured and arranged so as to ensure synchronization of the voltage and related characteristics such as phase being outputted from the FESS array with the voltage and related characteristics of the electrical power on the power distribution network.

Although a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.

Incorporation by Reference

All patents, published patent applications and other references disclosed herein are hereby expressly incorporated by reference in their entireties by reference.

Equivalents

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents of the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims. 

What is claimed is:
 1. A method for controlling AC frequency of electrical power being distributed to an electrical distribution network that is connected to one or more electrical loads and to one or more power sources, the frequency control method comprising the steps of: electrically coupling an energy storage sub-system to the electrical distribution network, said energy storage sub-system including one or more flywheel energy storage systems; controlling operation of each of the flywheel energy storage systems responsive to total power being outputted by the one or more power sources and a total load imposed by the one or more loads, so the electrical storage subsystem outputs an amount of electrical energy to the electrical distribution network so as to regulate the AC frequency of the electrical power being distributed to the electrical distribution network so as to be at or about a desired AC frequency.
 2. The frequency control method of claim 1 wherein said controlling includes controlling operation of each of the flywheel energy storage systems so as to reduce the amount of power being outputted to the electrical distribution network by the energy storage sub-system a determined amount, when the total power being outputted by the one or more power sources exceeds the total load imposed by the one or more loads, and by increasing the amount of power being outputted to the electrical distribution network by the energy storage sub-system by another determined amount, when the total power being outputted is less than the total load, wherein the determined amount and the another determined amount are determined by evaluating a difference between the total power and the total load.
 3. The frequency control method of claim 2, wherein the difference between the total power and the total load is determined periodically and wherein said controlling includes controlling operation of each of the one or more flywheel energy storage systems responsive to the periodically determined difference.
 4. The frequency control method of claim 1, further comprising the step of: determining a difference between the total power being outputted by the one or more power sources and the total load imposed by the one or more loads; and wherein said controlling includes controlling operation of each of the flywheel energy storage systems of the energy storage sub-system so as to maintain the AC frequency at or about a desired value by one of: increasing power being outputted by one or more flywheel energy storage systems when the determined difference is a negative value, or decreasing power being outputted by the one or more FESS energy storage sub-system when the determined difference is a positive value.
 5. The frequency regulation method of claim 1, wherein said electrically coupling includes electrically coupling a plurality of energy storage sub-systems to the electrical distribution network, each of said plurality of energy storage sub-system including a plurality or more of flywheel energy storage systems.
 6. The frequency regulation method of claim 1, wherein the energy storage sub-system includes one of 10 or more flywheel energy storage systems or 10 or less flywheel energy storage systems
 7. The frequency regulation method of claim 5, wherein each of the plurality of energy storage sub-systems includes one of 10 or more flywheel energy storage systems or 10 or less flywheel energy storage systems
 8. The frequency regulation method of claim 1, wherein the energy storage sub-system further comprises an adjustable load, and wherein said controlling includes controlling operation of each of the flywheel energy storage systems and the adjustable load responsive to the total power being outputted and the total load so as the electrical storage sub-system outputs the amount of electrical energy to regulate the AC frequency.
 9. The frequency regulation method of claim 8, wherein said controlling includes controlling operation of each of the flywheel energy storage systems and the adjustable load so as to one of inject power into the electrical distribution network or absorb power from the electrical distribution network to regulate the AC frequency.
 10. The frequency regulation method of claim 9, wherein said controlling includes controlling operation of each of the flywheel energy storage systems and the adjustable load so that a determined amount of power is diverted from the adjustable load so as to be outputted by the system to the electrical distribution network.
 11. The frequency regulation method of claim 10, wherein said controlling includes controlling operation of each of the flywheel energy storage systems and the adjustable load so that a determined amount of power also is outputted from the plurality of flywheel energy storage systems and thus outputted by the system to the electrical distribution network.
 12. The frequency regulation method of claim 9, wherein said controlling includes controlling operation of each of the flywheel energy storage systems and the adjustable load so that a determined amount of power is absorbed by the adjustable load from the electrical distribution network.
 13. The frequency regulation method of claim 12, wherein said controlling includes controlling operation of each of the flywheel energy storage systems and the adjustable load so that a determined amount of power also is absorbed by the plurality of flywheel energy storage systems from the electrical distribution network.
 14. An AC frequency regulation system for regulating AC frequency of electrical power being distributed to an electrical distribution network that is connected to one or more electrical loads and to one or more power sources, said system comprising: a plurality or more of flywheel energy storage systems, the plurality or more of flywheel energy storage systems being electrically coupled to the electrical distribution network; a controller being operable coupled to each of the flywheel energy storage systems and being responsive to frequency regulation signals generated external to said system; and wherein said controller is configured and arranged to control operation of each of the plurality or more of flywheel energy storage systems responsive to the frequency regulation signals, so said system one of outputs an amount of electrical energy to the electrical distribution network or absorbs an amount of electrical energy from the electrical distribution network so as to regulate the AC frequency of the electrical power being distributed to the electrical distribution network so as to be at or about a desired AC frequency.
 15. The AC frequency regulation system of claim 14, wherein the plurality or more of flywheel energy storage systems are arranged to form an array and wherein the array of the plurality or more of flywheel energy storage systems is controlled by the controller so that the array one of outputs power or absorbs power.
 16. The AC frequency regulation system of claim 14, wherein the system further comprises an adjustable load that is operably coupled to the controller and wherein the controller is configured and arranged so as to control one of the adjustable load and the plurality or more of flywheel energy storage systems so the system selectively outputs power or absorbs power responsive to the frequency regulation signals.
 17. The AC frequency regulation system of claim 15, wherein the system further comprises an adjustable load that is operably coupled to the controller and wherein the controller is configured and arranged so as to control one of the adjustable load and the array of the plurality or more of flywheel energy storage systems so the system selectively outputs power or absorbs power responsive to the frequency regulation signals.
 18. The AC frequency regulation system of claim 16, wherein the controller controls the adjustable load and the plurality or more of flywheel energy storage systems so that a determined amount of power is diverted from the adjustable load so as to be outputted by the system to the electrical distribution network.
 19. The AC frequency regulation system of claim 17, wherein the controller controls the adjustable load and the array of flywheel energy storage systems so that a determined amount of power is diverted from the adjustable load so as to be outputted by the system to the electrical distribution network.
 20. The AC frequency regulation system of claim 18, wherein the controller controls the adjustable load and the plurality or more of flywheel energy storage systems so that a determined amount of power also is outputted from the plurality of flywheel energy storage systems and thus outputted by the system to the electrical distribution network.
 21. The AC frequency regulation system of claim 19, wherein the controller controls the adjustable load and the array of flywheel energy storage systems so that a determined amount of power also is outputted from array of flywheel energy storage systems and thus outputted by the system to the electrical distribution network.
 22. The AC frequency regulation system of claim 16, wherein the controller controls the adjustable load and the plurality or more of flywheel energy storage systems so that a determined amount of power is absorbed by the adjustable load from the electrical distribution network.
 23. The AC frequency regulation system of claim 17, wherein the controller controls the adjustable load and the array of flywheel energy storage systems so that a determined amount of power is absorbed by the adjustable load from the electrical distribution network.
 24. The AC frequency regulation system of claim 22, wherein the controller controls the adjustable load and the plurality or more of flywheel energy storage systems so that a determined amount of power also is absorbed by the plurality of flywheel energy storage systems from the electrical distribution network.
 25. The AC frequency regulation system of claim 23, wherein the controller controls the adjustable load and the array of flywheel energy storage systems so that a determined amount of power also is absorbed by the array of flywheel energy storage systems from the electrical distribution network.
 26. An AC frequency regulation system for regulating AC frequency of electrical power being distributed to an electrical distribution network that is connected to one or more electrical loads and to one or more power sources, said system comprising: a plurality or more of flywheel energy storage systems, the plurality or more of flywheel energy storage systems being arranged to form an array, where the array of the plurality or more of flywheel energy storage systems is electrically coupled to the electrical distribution network; an adjustable load; a controller being operable coupled to each of the plurality of flywheel energy storage systems of the array and the adjustable load, the controller being responsive to frequency regulation signals generated external to said system; and wherein said controller is configured and arranged to control operation of each of the plurality or more of flywheel energy storage systems of the array and the adjustable load, responsive to the frequency regulation signals, so said system one of outputs an amount of electrical energy to the electrical distribution network or absorbs an amount of electrical energy from the electrical distribution network so as to regulate the AC frequency of the electrical power being distributed to the electrical distribution network so as to be at or about a desired AC frequency.
 27. The AC frequency regulation system of claim 26, wherein the controller controls the adjustable load and the plurality or more of flywheel energy storage systems of the array so that a determined amount of power is diverted from the adjustable load so as to be outputted by the system to the electrical distribution network.
 28. The AC frequency regulation system of claim 27, wherein the controller controls the adjustable load and the plurality or more of flywheel energy storage systems of the array so that a determined amount of power also is outputted from the plurality of flywheel energy storage systems and thus outputted by the system to the electrical distribution network.
 29. The AC frequency regulation system of claim 26, wherein the controller controls the adjustable load and the plurality or more of flywheel energy storage systems so that a determined amount of power is absorbed by the adjustable load from the electrical distribution network.
 30. The AC frequency regulation system of claim 22, wherein the controller controls the adjustable load and the plurality or more of flywheel energy, storage systems of the array so that a determined amount of power also is absorbed by the plurality of flywheel energy storage systems from the electrical distribution network.
 31. The AC frequency regulation system of claim 26, wherein the plurality or more of flywheel energy storage systems are arranged so as to form a plurality or more of arrays, each of the plurality or more arrays including a plurality or more of flywheel energy storage systems.
 32. The AC frequency regulation system of claim 26, wherein the array comprises 4 or more flywheel energy storage systems.
 33. The AC frequency regulation system of claim 26, wherein the array comprises 7 or more flywheel energy storage systems.
 34. The AC frequency regulation system of claim 26, wherein the array, comprises 10 flywheel energy storage systems.
 35. The AC frequency regulation system of claim 26, wherein each of the plurality of arrays array comprises one of 4 or more flywheel energy storage systems, 7 or more flywheel energy storage systems, or 10 flywheel energy storage systems.
 36. The AC frequency regulation system of claim 31, wherein the system comprises 40 arrays of flywheel energy storage systems. 